Has the pill changed the rules of sexual attraction?

The contraceptive pill alters monthly fluctuations in hormones associated with the menstrual cycle, mimicking the more stable hormonal conditions associated with pregnancy. This might not only disrupt the natural processes which influence women's choice of partner, but it could also make them less able to compete with women who have a natural menstrual cycle, a paper published this week in Trends in Ecology and Evolution suggests.

How worried should we be, and what other strategies can men and women use to tip the odds in their favour? New Scientist investigates.

What do we know about how women choose a mate?

Recent studies have confirmed that women tend to prefer taut bodies, broad shoulders, clear skin and defined, masculine facial features – all of which may indicate sexual potency and good genes. Women also tend to be attracted to men who look as if they have wealth, or the ability to acquire it.

Levels of the sex hormones oestrogen and progesterone fluctuate throughout a woman's monthly menstrual cycle. At the start of the cycle – when the egg is maturing – the body releases oestrogen. During the second half of the cycle, after the egg has been released and might implant, progesterone is secreted. A woman's most fertile period comes in between these two phases, shortly before and immediately after the egg is released.

Women's preferences for certain male scents and features are thought to change during their cycle. For example, as they approach ovulation, women prefer men with more masculine features, possibly because these reflect high sexual potency and better genes. During non-fertile periods they prefer more feminine facial features and attributes, perhaps because such men may be more nurturing and therefore better at helping to raise children, even if they are not their own.

The pill may throw a spanner in the works. It stops this cyclical release of oestrogen and progesterone, and so may interfere with women's natural choice of partner. Some studies have suggested that while women usually prefer the scent of men with immune profiles dissimilar to their own, those on the pill preferred men with similar immune profiles.

Should women on the contraceptive pill be worried?

Although studies have hinted that women's choice of partner may be affected by the pill, such basic mechanisms of mate choice likely evolved in very different conditions to today's society. Our ancestors lived in far smaller communities and rarely had the chance to meet outsiders. This means the chances of inbreeding would have been much higher, and subtle cues like smell might well have reduced the chances of this happening.

Today, our communities are far more diverse, so the chances of inbreeding are more remote. Many would argue that personality is a far better way to choose a life partner than what they smell like. One recent study involving speed-dating experiments suggested that although women might say they prefer the scent of men with dissimilar immune systems, this doesn't correspond with the men they actually chose to go out with.

As the authors of the new Trends in Ecology and Evolution paper point out, more studies are needed to establish whether mate preferences in lab experiments actually correlate with how men and women behave in the real world.

Don't men have any say in the matter?

As a general rule, men tend to desire women with features that suggest youth and fertility, including a low waist-to-hip ratio, full lips and soft facial features.

The contraceptive pill might in theory iron out some of these differences. The problem is that many of these studies have relied on artificial conditions – by asking men to rate women's walks in video clips, for example.

It's unlikely that we pay such close attention to these cues in the real world. Even if we do, it's obvious that the majority of women who are on the pill have no problem attracting or retaining a partner. In the case of the lap dancers, those on the pill earned similar tips to those with normal cycles during the non-fertile periods of their menstrual cycle, suggesting that men found them equally attractive.

Is there anything men can do to make themselves more attractive to women?

If all else fails, try surrounding yourself with beautiful female friends or slipping a wedding ring on your finger. Both men and women find members of the opposite sex more attractive, if others seem attracted to them too.

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